Abstract:

To improve the gas-solid two-phase mixing and eliminate the effect of secondary flow on the back-mixing near the riser wall in the feedstock injection zone, a novel fluidizer technology is proposed. A protective layer is produced by fluidizer to prevent long-duration contact between catalysts and feed near the wall. Three schemes for this technology (reverse-impact, concurrent-flow and crossed schemes) are used to improve the catalyst-feed mixing and back-mixing near wall by using 3-D CFD simulation. The amount of fluidizer of the optimal scheme is further optimized. The results show that the best is the reverse-impact scheme and the worst is the crossed scheme. The optimal reverse-impact scheme(when the mass flux of fluidizer is equal to the 15% mass flux of feed) can improve the catalyst-feed mixing, prevent the expanding of secondary flow and weaken the intensity of back-mixing at the |r/R|>0.9 near the wall.

Key words: riser, feed injection zone, secondary flow, fluidizer, fluid catalytic cracking, EMMS, CFD

摘要：

为改善提升管进料区气固两相混合状况、消除二次流对近壁面处返混的影响，提出了一种新型助流剂技术。该技术在边壁处形成一层助流剂“保护层”，可阻止进料射流与催化剂在边壁处过长接触。通过三维CFD模拟对比了3种助流方式（逆流式、顺流式、交叉式）对传统进料区催化剂与进料混合和边壁返混的改进效果，并对最佳方式下助流剂量做进一步的优化。结果表明，逆流式助流方式最理想，交叉式助流方式最差。合适的逆流式助流方式（如助流剂注入量为进料相总流率的15%时）可改善进料区催化剂与进料相混合，抑制二次流扩张，明显减弱近边壁处（|r/R|>0.9）返混强度。

关键词: 提升管, 进料区, 二次流, 助流剂, 流化催化裂化, 能量最小多尺度模型, 计算流体力学